Brewing Water Chemistry Calculator

Why water matters in beer

The mash and the boil are essentially a chemistry lab where dissolved minerals shape pH, enzyme activity, hop bitterness perception, and the malt-vs-hop balance of the finished beer. Two breweries using the same recipe with different water can produce noticeably different beers. The IPA-friendly water of Burton-on-Trent and the soft Pilsner water of Plzeň are textbook examples of how source water shaped entire beer styles.

The four ions that matter most

The sulfate-to-chloride ratio is the single most discussed water number in homebrewing. Higher SO₄ (Burton style, 2:1 to 4:1) accentuates hops; higher Cl (London or Munich style, 1:2) accentuates malt.

The calculator on this page works on calcium, and reports the sulfate and chloride that come along with whichever salt you pick. Magnesium is in the table above because it belongs in any discussion of brewing water, but you rarely need to add it: a normal grain bill already contributes 50 to 60 ppm of magnesium to the mash on its own, and Epsom salt is only worth reaching for if you are building from reverse osmosis and want a touch more.

The math for additions

Read the units on any salt figure before you use it. Most American brewing books quote grams per gallon; the numbers below are grams per liter, which is what this calculator asks for. They differ by a factor of 3.785, and mixing them up is the single easiest way to wreck a batch of water.

Those come straight out of the molecular weights. Gypsum is 172.2 g/mol and calcium is 40.08 of it, so a gram dissolved in a liter puts 40.08/172.2 = 23.3% of a gram of calcium into that liter, which is 232.8 mg/L, and ppm and mg/L are the same thing in water.

To add 50 ppm calcium across a 20 L batch with gypsum:

grams_needed = (50 ÷ 232.8) × 20 = 4.3 g

That gypsum addition also bumps sulfate by 50 × (557.9 ÷ 232.8) = 120 ppm. You cannot raise calcium with these salts without bringing sulfate or chloride along for the ride.

Buy the dihydrate, and check the label

Calcium chloride sells in two forms. The dihydrate (CaCl₂·2H₂O) is the flaky, damp one homebrew shops stock, and it is what the figures above assume. Anhydrous calcium chloride is a harder pellet used as a road-salt and desiccant, and it is 32% stronger per gram: 361 ppm Ca²⁺ and 639 ppm Cl⁻ in a liter. If your bag came from a hardware store rather than a brew shop, weigh out about three quarters of what this page tells you.

Calcium chloride is also hygroscopic. An open tub that has been sitting in a humid garage for a season has pulled in water and no longer weighs what the chemistry says, which is a good reason to buy it in small quantities.

Style-typical water profiles

Start with reverse osmosis if you can

If your tap water is hard, full of chloramine, or wildly variable by season, the cleanest path is to start with RO water (cheap from a supermarket vending machine, or run a small under-sink RO membrane at home) and build your profile from zero. You only need to know the four minerals you added, not whatever your municipal water department put in this month or next.